1. Field of the Invention
This invention relates to a technique device for forming an image, specifically, to a video interfacing technique in an image forming device having video and engine controllers.
2. Description of the Related Art
Generally, image forming devices, such as laser printers, plain paper facsimile machines, and inkjet printers, print images corresponding to data received from an external system, such as a host computer. These image forming devices have video and engine controllers. These devices print images corresponding to the encoded image sent to them according to the following process:
First, the video controller of the image forming device converts encoded information from the external system into image data that the image forming device can process, and then transmits the image data. The engine controller receives the image data from the video controller, and prints the image on paper. Referring to the structure of a laser printer having video and engine controllers, the input-output signal correlation between the video and engine controllers is set forth in the following description:
A laser printer, for example, includes a video control unit and an engine control unit and an operating panel equipment (OPE). The video control unit has a computer interface for interfacing with the host computer and a video controller connected to the computer interface and OPE and an engine interface connected to the video controller. The engine control unit includes a video interface connected to the engine interface for interfacing signals therebetween. The video control unit also includes an engine controller connected to the video interface and an input/output (I/O) interface connected to the engine controller for interfacing the engine controller with a sensor circuit, a machinery driving unit, and an electrophotography unit, these three elements also being contained in the engine control unit.
The video controller includes a control program stored in a read only memory (ROM) and a random access memory (RAM) needed for various purposes including buffering information transmitted between the host computer and the OPE. The video controller converts data received through the computer interface into image data and then transmits it to the engine control unit. The engine interface interfaces the engine control unit and the video controller so that input/output signals can be transferred under the control of the video controller. The OPE, which is controlled by the video control unit, has a display and multiple keys for entering various commands. The engine control unit is connected to the video control unit. The video interface allows for the transmission and reception of signals between the video control unit and the engine controller. The engine controller controls the machinery driving unit and electrophotography unit according to the instructions of the video control unit and prints the image corresponding to the image data received from the video control unit. It also senses the operating conditions of the engine control unit such that as the condition of the paper supply and transfer through the sensor circuit. The sensor circuit receives input from various sensors for monitoring the printing process, such as the state of the paper supply and transfer, the amount of developer, etc., and sends this information to the engine controller. The machinery driving unit operates various mechanisms for paper supply and transfer and printing according to the instructions of the engine controller. The electrophotography unit prints the image corresponding to the image data on paper using an electrophotographic developing process. Numerous signals are transferred between the video controller and the engine controller. Unfortunately, errors can occur because of internal or external factors such as abnormally high voltages, static electricity, and the reception of a wrong command message. In short, errors can occur which can interrupt the operation of the video controller and the engine controller. Under these conditions, the electrical power needs to be temporarily interrupted to completely reset the laser printer, thereby involving inconvenience and the problem of a delay for the warm-up of the printer after being reset.
The following patents each discloses features in common with the present invention but do not, however, teach or suggest the specifically recited technique of the present invention: U.S. Pat. No. 5,270,774 to Kikuchi, entitled Testing Device For Electrophotographic Imaging Apparatzis, U.S. Pat. No. 5,023,631 to Negishi et al., entitled Stopping Process Control Device, U.S. Pat. No. 5,243,380 to Pesar et al., entitled Board Fault Isolation Technique, and U.S. Pat. No. 5,398,100 to Ishizu et al., entitled Image Recording Apparatus Operable With A Vertical Scan Synchronization Signal.